On the possibility of local buckling of the surface of an elastic half-space under compression

The possibility of local buckling of the free surface of the lower half-plane under compression is studied in a static formulation within the framework of plane deformation. It is shown that in some media small subcritical strains can lead to local buckling of the half-plane surface. It is found that two forms of local surface buckling correspond to one critical compression load. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 3, pp. 149–152, May–June, 2005.     

Influence of heat conduction on the unlimited shockless compression of a flat gaseous layer

A numerical investigation is made of the influence of heat conduction on the compression of a flat gaseous layer in which, in the case of an ideal adiabatic gas, shockless compression occurs with unlimited cumulation of density and energy. Approximate formulas are obtained that characterize the asymptotic behavior of the cumulation of energy and density and of the energy expended on compression. It is shown that the phenomenon of density and energy cumulation is preserved when heat conduction is taken into account. Institute of Technical Physics, Snezhinsk 456770. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 39, No. 4, pp. 25–32, July–August, 1998.     

Strength of water under pulsed loading

Experiments were performed to study the strength of water under conditions of pulsed extension, which is typical of the interaction between a triangular compression pulse and a free surface. The tests were performed in a wide (40–1000 MPa) range of rariation in the amplitude of the compression pulse at deformation rates of 10⁴−10⁵ sec⁻¹. It is found that as the compression-pulse amplitude increases from 150 to 1050 MPa, the strength of water decreases from 46 to 22 MPa. The deformation rate was found to have little effect on the strength. The possibility of using the model of homogenous nucleation (formation of cavitation nuclei) to interpret the data obtained is discussed. Institute of Chemical Physical, Russian Academy of Sciences, Chernogolovka 142432. Translated from Prikladmaya Mekhanika i Tekhnicheskaya Fizika, Vol. 41, No. 4, pp. 198–205, July–August, 2000.     

On the accuracy of a MJPEG-based digital image compression PIV-system

 In this communication, the Digital Image Compression (DIC) – PIV system is introduced. The present system allows the measurement of mean and RMS velocities in turbulent flow fields, using JPEG digital image compression technique for on-line recording of thousands of images. The decompression and subsequent analysis of the images, performed by means of digital cross-correlation technique, is carried out off-line. Errors incurred by the application of the compression method are assessed and discussed. The effect of the compression is firstly analysed by linearly traversing (synthetic) computer-generated PIV-images at constant velocity. Secondly, accurate LDA measurements and data from direct numerical simulation (DNS) are used as a basis for the analysis in a low Reynolds number open water channel flow. The results show that excellent agreement between LDA and DIC–PIV measurements for mean and RMS velocities can be achieved using a compression factor up to 12. Received: 27 August 1996 / Accepted: 15 December 1998     

Measurement of Capillary Pressure–Saturation Relationships Under Defined Compression Levels for Gas Diffusion Media of PEM Fuel Cells

Measurements of capillary pressure–saturation relationships under defined levels of compression for gas diffusion layers (GDL) of polymer electrolyte membrane fuel cells as thin, mixed-wettable porous media have been carried out in a newly constructed device. This article lines out the construction principle of the cell and the preconditioning procedure of the sample to measure the capillary pressure–saturation relationships under well-defined conditions and loads of compression. Three commercial GDLs (Freudenberg H2315T10A, H2315T10AC1, and SGL Carbon BA24) have been examined and a compression-depending hysteresis of the capillary pressure–saturation relationship has been measured and identified.     

Two alternatives of magnetic cumulation

This paper deals with phenomena leading to a considerable increase in magnetic field and energy density during compression of a magnetic flux trapped by a conducting shell and joint deformation of a magnetic field and material. The main features and merits of these two alternative schemes of magnetic cumulation are discussed. A comparison is made between the classical and schock-wave schemes of magnetic compression in a material with a phase transition from a nonconducting to a conducting state. The possibility of magnetic-energy cumulation during stretching of magnetic field line by a transverse flow of a conducting material is considered. Lavrent’ev Institute of Hydrodynamics, Russian Academy of Sciences, Novosibirsk 630090. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 41, No. 5, pp. 32–47, September–October, 2000.     

Optimum overtaking compression shocks with restrictions imposed on the total flow-deflection angle

The problem of optimization of gasdynamic variables behind a system of two steady oblique compression shocks with restrictions imposed on the flow-defection angle is considered. The intervals of input parameters, in which this system turns out to be more effective than one shock, are determined. On the basis of an analysis of the system optimal for the static pressure, the physical meaning of the transition from one type of the reflected discontinuity to another is explained for the problem of interaction of overtaking oblique compression shocks. Baltic State Technical University, St. Petersburg 198005. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 40, No. 4, pp. 99–108, July–August, 1999.     

Decay of a centered prandtl-mayer compression wave in a steady gas flow

Discontinuity decay at a singular point of a centered compression wave is considered. Analytical solutions are given that allow one to determine the type of reflected discontinuity that issues from the point of decay and the boundaries of ranges of parameters within which a solution of the problem exists. Baltiisk State Technical University, St. Petersburg 198005. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 39, No. 3, pp. 59–68, May–June, 1998.     

Strain diagrams for uranium and its alloy with molybdenum in dynamic uniaxial compression and tension and at elevated temperatures

Systematic results from studies of dynamic diagrams of uniaxial compression and tension of uranium-238 and its alloy with molybdenum at various strain rates and temperatures are presented. The data allow one to plot stress curves versus strain, strain rate, and temperature for uniaxial compression-tension and to develop mathematical models describing the behavior of materials under various loading conditions most completely. All-Russia Research Institute of Experimental Physics, Sarov 607190. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 40, No. 6, pp. 197–203, November–December, 1999.     

Estimate of the strength of a plate with an elliptic hole in tension and compression

The strength of a plate with an elliptic hole under uniaxial tension or compression is estimated for arbitrary angles between the ellipse axes and the direction of loading with the use of the gradient strength criterion. The calculated critical stress agrees with the existing experimental data. Institute of Physicotechnical Problems of the North, Siberian, Division, Russian Academy of Sciences, Yakutsk 677891. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 41, No. 3, pp. 163–168, May–June, 2000.     

The impact of non-DLVO forces on the onset of shear thickening of concentrated electrically stabilized suspensions

This paper exposes an extension of an activation model previously published by the authors. When particles arranged along the compression axis of a sheared suspension, they may overcome the electrostatic repulsion and form force chains associated with shear thickening. A percolation-based consideration allows an estimation of the impact of the force chains on a flowing suspension. It suggests that similar to mode coupling models, the suspension becomes unstable before the critical stress evaluated from the activation model is reached. The percolated force chains lead to discontinuous shear thickening. The model predictions are compared with results from two experimental studies on aqueous suspensions of inorganic oxides; in one of them, hydration repulsion and in the other hydrophobic attraction can be expected. It is shown that the incorporation of non-Derjaguin–Landau–Verwey–Overbeek forces greatly improve predictions of the shear thickening instability.     

Suppression of oscillations of piston-aided wind tunnels

The method chosen to compensate for the forces acting on the barrel in the course of compression and confinement of the test gas in the settling chamber of a hypersonic wind tunnel with a free locking piston is justified. A method is proposed to compensate for the effect of adverse factors by optimizing the mass of an auxiliary piston introduced into the system. The effectiveness of the method is validated experimentally. As a result, for the case of gas compression to 200 MPa, the displacement of the center of mass of the barrel is reduced from 50 to 0.25 mm, which is smaller than the amplitude of elastic axial extension corresponding to the maximum pressure of the gas. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 5, pp. 212–220, September–October, 2008.     

Numerical modeling of the thermomechanical behavior of steels with allowance for the propagation of Luders bands

A thermomechanical model based on physical representations of the motion of dislocation continuum and a model for the initiation and propagation of plastic shear are proposed to describe slow flows of the type of Luders bands. Two-dimensional calculations of Luders band propagation are performed for HSLA-65 steel samples under compression at various strain rates and temperatures. The calculation results are in good agreement with experimental data. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 5, pp. 146–155, September–October, 2007.     

Effect of streamwise structures on heat transfer in a hypersonic flow in a compression corner

Coefficients of heat transfer to the surface in a laminar hypersonic flow (M _∞ = 21) over plane and axisymmetric models with a compression corner are presented. These coefficients are measured by an infrared camera. The parameters varied in the experiments are the angle of the compression corner and the distance to the corner point. Characteristics of the flow with and without separation in the corner configuration are obtained. The measured results are compared with direct numerical simulations performed by solving the full unsteady Navier-Stokes equations. Experiments with controlled streamwise structures inserted into the flow are described. A substantial increase in the maximum values of the heat-transfer coefficient in the region of flow reattachment after developed laminar separation is demonstrated. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 4, pp. 112–120, July–August, 2009.     

On universal deformations in analysis of Signorini’s nonlinear theory of hyperelastic media

It is shown that uniform compression/tension and simple shear as universal deformations are quite useful in studying Signorini’s nonlinear theory of hyperelastic materials. They make it possible to formulate restrictions for the elastic constants of the theory and to explain the Poynting effect __________ Translated from Prikladnaya Mekhanika, Vol. 43, No. 12, pp. 54–60, December 2007.     

Stresses in a weighable half-plane with a semicircular notch

The influence of the surface roughness on the stress state of a rock is studied. For an elastic half-plane in the gravity field that contains a notch shaped like a semicircle, the stress distribution is constructed. It is shown that depending on the Poisson ratio, the notch bottom can be in a state of tension or compression. The polynomial dependence of pressure on depth is given on the axis of symmetry. Novosibirsk State University, Novosibirsk 630090. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 41, No. 1, pp. 152–161, January–February, 2000.     

Enhanced nonlinear 3D Euler–Bernoulli beam with flying support

Using Hamilton’s principle the coupled nonlinear partial differential motion equations of a flying 3D Euler–Bernoulli beam are derived. Stress is treated three dimensionally regardless of in-plane and out-of-plane warpings of cross-section. Tension, compression, twisting, and spatial deflections are nonlinearly coupled to each other. The flying support of the beam has three translational and three rotational degrees of freedom. The beam is made of a linearly elastic isotropic material and is dynamically modeled much more accurately than a nonlinear 3D Euler–Bernoulli beam. The accuracy is caused by two new elastic terms that are lost in the conventional nonlinear 3D Euler–Bernoulli beam theory by differentiation from the approximated strain field regarding negligible elastic orientation of cross-sectional frame. In this paper, the exact strain field concerning considerable elastic orientation of cross-sectional frame is used as a source in differentiations although the orientation of cross-section is negligible.     

Mathematical model of a heterogeneous medium consisting of a matrix and spherical inclusions

A mathematical model of a heterogeneous medium consisting of an elastoplastic matrix and elastic spherical inclusions is constructed. The model takes into account plastic zones, which appear in the vicinity of the inclusions. It is shown that when the effect of plastic zones is taken into account, the averaged “moduli” of volume compression, shear, and yield strength depend not only on the volume concentrations of the inclusions, but also on the mean pressure in the medium. Institute of Theoretical and Applied Mechanics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 40, No. 4, pp. 170–178, July–August, 1999.     

Numerical simulation of stabilization of the boundary layer on a surface with a porous coating in a supersonic separated flow

Stability of a supersonic (M _∞ = 5.373) boundary layer with local separation in a compression corner with a passive porous coating partly absorbing flow perturbations is considered by solving two-dimensional Navier-Stokes equations numerically. The second mode of disturbances of a supersonic boundary layer is demonstrated to be the most important one behind the boundary-layer reattachment point. The possibility of effective stabilization of these disturbances behind the reattachment point with the use of porous coatings is confirmed. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 2, pp. 39–47, March–April, 2007.     

Experimental investigation of the stability of reinforced cylindrical shells subject to axial compression

The paper presents the results from experimental study of the influence of reinforcement (rectangular plates) on the buckling loads and stresses of two sets of cylindrical shells subject to axial compression __________ Translated from Prikladnaya Mekhanika, Vol. 42, No. 5, pp. 117–119, May 2006.